Rubber composition



March 18 1941. J pA-rmCK v 2,235,621

RUBBER COMPOSITION Filed March 1'?, 1958 Na.+NcLX fl S I s e sH+es+aNoH,fnl/effing. Ese/,A C. [Caino/U Patented Mar. 18, 1941 PATENT OFFICERUBBER COMPOSITION Joseph C. Patrick, Morrisville, Pa., assignor toThiokol Corporation, Yardville, N. J., a corporation of DelawareApplication March 17, 1938, Serial N0. 196,376

' 3 Claims. This invention relates to a reaction whereby natural rubberand various varieties of syn-- thetic rubbers may be vulcanized or curedby the use of a chemical compound containing sulfur as one of itssubstituents. For many years, in fact ever since the discovery ofvulcanization by Goodyear, elementary sulfur has been widely employed asa. vulcanizing agent for rubber and, while of the greatest utility inthis process, the

1o use of sulfur as a vulcanizing agent is attended with certain verydenite disadvantages. For

- example, numerous rubber articles, e. g. footwear and pneumatic tiresdevelop, after manulfacture, a deleterious eiect known as bloomi5 ing,which greatly impairs Ithe value of such articles.

Other instances in which the blooming of sulfur is of greatdisadvantage'is in the process of retreading used tires. For thispurpose, rubber manufacturers sell a vulcanizable composition of sulfurand rubber to repairmen. This is sold in the form o1' sheets or strips.The process of retreading includes the step of superimposing a strip ofla vulcani'zable rubber composition. on the tread portion of an old tireand forming a union between the two under heat and pressure.l Thevulcanzable retreading stock is frequently stored in the -repairmansshopfor a long period, and when sulfur is the vulcanizing agent, suchstock develops the disadvantages of the blooming effect alreadymentioned. The eiect of this blooming is serious because it tends toprevent a proper union between Ithe surface of retreading stock and thesurface of the old tire.

Another disadvantage of sulfur as a vulcanizing agent is that thevaluablel properties produced by vulcaniaation, such as' tensilestrength; elongation, etc. are subject to reversion, i. e. there is anoptimum period of cure and if this period is 40 exceeded, there is amarked deterioration.

Still another disadvantage of sulfur is the' fact that an excess ofsulfur is 4required over and above that which actually combines with therubber. The presence of this excess gives the rubber composition pooraging properties and much eiont has been expended in endeavoring tostabilize the vulcanized composition such as by the addition ofantioxidants.

It is an object of this invention to provide a 5o rubber compositionfree from the phenomenon of blooming. a

Another object is to provide such a composition substantially free fromfree sulfur.

Another object is to obtain a rubber composi- 55 tion having improvedphysical properties.

Another object is to'provide a rubber composition the properties ofwhich are stable upon aging. v l

Another object is to provide a rubber composition which is not subjectto the phenomenon 5 of reversion.

Another object is to provide a rubber composition in which apredetermined rate of vulcanization can be obtained independently of theextent or coeiiicient of vulcanlzation.

Other objects and advantages'will appear herea inafter.

The advance in the art represented by the invention will be dened by theclaims ultimately appended hereto. Of the numerous forms in ll which theinvention thus dened may be embodied, a considerable number will bedescribed herein for purposes of illustration.

In accordance with this invention, certain classes of organic polysulldepolymers are em- 20 ployed as described and claimed.

The structure of these polymers may be describedgenerally by statingthat they are characterized, in part, by an organic radical selectedfrom certain groups of organic compounds, al- 25 ternating with a groupof sulfur atoms, and the general ,formula of such polysulde polymers maybe written as follows:

Traulyide poly mer As is more fully hereinafter explained, the pair ofsulfur atoms separating the radicals R in the.

above-formulae are in stable chemical combination and form the linkagebetween the said radicals, whereas the remaining sulfur atoms joined tothe said pairare in a labile conditionand it is this labile conditionwhich enables those parhrw-ing certain characteristics.

ticular. sulfur atoms to function as the active vulcanizing agent. i.fIl-heunit ofthe saidpolymersisR-SgwhereSisasuMuratom,nis3to6andRisa-mdil The intervening structure is nothowever limited to members of the groups set forth and may include otherstructure, e. g. ketone structure.

IIhe said polymers may be formed by dierent means, all of whichsubstantiate the constitution of said polymers as shown above. Forexample, a suitable polymer may be formed by a reaction between analkaline polysulnde. e. g. sodium, po-

tassium, ammonium, lithium, etc. polysuliide, -onthe one hand, and onthe other hand an organic compound containing. a substituent on each of-two diil'erent carbon atoms where those carbon atoms are joined to andseparated byintervening structure as above set forth. which substituentis split on' during the reaction. In other words. there is a pair otcarbon atoms to which are joined. respectively. a substituent capable of`being split oil? lby reaction with an alkaline D01?- sulfide. 'IheVspace between :the carbon atoms is opened up and intervening structureis placed in that space. Each cnr-bon wtom is joined, on the one hand toa substituent capable or! being split oil.' by an alkaline polysultldeand on the otherhandto structure intervening `pair of carbon atoms.

In the polysul-de reaction .the molecules oi the organic substancebecome ioined together to form la complex pattern or' chain, i. e. therelatively sm molecules of the organic substance are joined together toform a very iarge'molecule or polymer. lThis jolnder takes place throughthe medium of the sulfur in the polysuifide. .Th-is sulfur acts as asort of bridge from one molecule to the next. As a result, the reactionproducts have high percentages of sulfur. They also have colloidalproperties.

The mechanism ot the polysulde reaction will now be explained, referencebeing had to the accompanying diagram.

Reaction A curs because .the Na (sodium) unites with the X atom 4or" i.e. splits ol! the said X' aftom or radicar from the compound cationreaction.

Inreaictions AandBabove,XandX' alterebetween the said speetiveiy .anyscponrnlbie acidic substituent. i. e.

substituents which can be split oil! by treatment with an alkalinesubstance. e. 8. halogen, sulfate, nitrate, phosphate, carbonate,formate, wetwte.

stearate, crainte, malon'ste, tartrate, citrate, etc.

As a result .of A, a molecule is produced having a saponinablesubstituent attached to one carbon atom, and a sodium polysuliide 4(ffii) v with the saponirloble acidic substituent. the compound producedin Equation A has'the remarkable ability of 'uniting with itself, asshown in: Eqmtion B.

Moreover, the compound produced as shown' in Equation B unites withitself in the same manner and this continues until the size of themolecule is so large that its sluggishness prevents further condensationor self-union.

This ability requires the existence of a sodium polysulnde radical (orits equivalent) on one car bon atom and a saponinable acidic substituenton another carbon atom of the same compound.

If .this -'rule is observed, union of the compound containing said pairot carbon atoms to form ampound containing. a tetrad or quartet ofcarbon atoms does not exhaust the reaction because each terminal carbonatom of this quartet willalso have attached thereto, respectively, asaponiable substituent and a sodium polysuliide radical, so thait thequartet or tetrad'cen form an octad.

'This permits a building -up of a carbon chain in geometrical startingwith a compound containing (burt not ny'consisting of) two carbon 'Theradical R `previously referred to is the vention, the 'two carbon atomsin .that radical should be .by and ioined to intervening structureselected from the group consisting `(a) Ether linkages tb) Ummm '.(c)Arylgroupsorarommtiesiructure (d) Satin'ated hydrocarbons asl previouslymentioned.

These two carbon dans are respectively attached to substituents whichare split oi! in the reaction as will be explained The unit ofthe chainis the said pair o! ciu-bonl atoms, separated by andattached to saidintervening structure, plus a group of sulfur atomsthus:

Q s I 21... i-'sl A I where the group oi sulfur atoms is the' tetra-vsulnde group. This group may be the disulfide group -SS, the trisulildegroup the tetrasulfide group shown, the pentasuliide group il s or thehexasuliide group have a male thread andthe other a female thread. Themale member on one unit can then engage the female member on anotherunit, so as to build up a chain or complex structure analogous to thepolymer of this invention.

-There must be at least two of such interlocking members on each unit.Otherwisethe length of the chain is limited to a union of two elements.

Referring now to the diagram, the compound shown as produced in reactionB continues to unite with itself until a long chain is built up havingthe formula shown at C. This then loses its X terminal and acquires SHterminals at each end by hydrolysis, as shown in Equations D and E. Atthis stage the condensing or polymerizing action of the polysulfidesubstantially ceases.

It is desirable to carry out the above reaction in an alkalinedispersion medium as specifically illustrated in Example l below, and toproduce the polymer atthe above mentioned stage i'n the form of alatex-like liquid from which the polymer may be separated by variousmeans, e. g. coagulation produced by the addition of acid. 'I'his latexhas the property of mixing intimately with water without dissolvingtherein and may or by employing any-of a number of oxidizingv agentseffective under alkaline conditions, such as hydrogen, peroxide,lbenzoyl peroxide, sodium, potassium, barium and calcium peroxides,perborates, permanganates, chromates and dichromates, etc.

When oxidized the polymer shown at E con' denses as indicated byEquation Fin the diagram. Alkaline` polysuldas are themselves oxidizingagents provided an excess be employed over the equimolecular proportionsshown. in Equations A to E inclusive.

' It is generally desirable to increase the size4 of the molecule asmuch as possible in the intermediate stage.

Proof that the reaction occurs bythe mechanism shown and that theproducts obtained have the formulae shown include the following:

(a) Taking BB dichlorinated ethyl ether as The an example, the chlorineof the compound appears quantitatively in the form of sodium p chlorideas a by-product. v

(b) After isolating the 'polymer from the soluble by-products the weightof the polymer is quantitatively equal to the weight of thedichlorinated ether4 minus the halogen plus the sulfur from the alkalinepolysulfide. I y

(c) The proportion of sulfur in the-polymer is equal to that in thefollowing formula:

(d) Attempts to determine molecular weight of the polymer shows that itis very high. 'I'his is substantiated by the properties as hereindescribed.

(e) A polymer having properties identical with those obtained byreacting dihalogenated ethyl ether with sodium tetrasulde, can beobtained by an entirelydifferent route, as shown bythe followingequations:

The above dimer-(rapto ethex` is obtained by reacting BB dichlorethylether with sodium hydrosulde NaSI-l. y

(2) 2(HS.R.S.S.R.SH) +0:

. HS.R.S.S.R.S.S.R.S.S.R.SH

This continues until a polymer is built uphaving the formula v 3) Hs.(Rss) asn This on further oxidation gives (4) HS. (RSS) nR.S.S.R (RSS)HS The above compound (4) reacts with sulfur tol produce a productidentical with that shown in Equation F in the diagram and converselythe product shown in Equation F can be partially desulfurized to producea product identical with that shown at (4) above.

The above mercaptan reaction shows that the linkage between the organiccarbon radical is through a sulfur bridge.

(f) X-ray examination shows that the distance between the carbonradicals is equal to the sum of the diameters of two sulfur atoms.

The two sulfur atoms referred 4to are. bound rmly and form the directbridge between the carbon radicals whereas the remaining sulfur atomsare in labile form and may be removed by a partial desulfurizing actionas already mentioned. A

In the formula shown in Equation F, the value of n is so greatthat theproduct is substantially Y and practicallya polymer of the unit 38] In...g

and the producty reacts* as such. For example, three mols of this unitreact vwith two mols of sodium sulfide according to the followingequation:

and the resultig product is identical in all its properties with the.product'produced by oxidation of a polyfunctional mercaptan as 4shown-in Equations 1 to 4 above. v

Conversely, the polymer shownin Equation i above as produced by.oxidation of a polyfunctional mercapt'an behaves substantially as apolymer of the unit H1... t Si] A mol of this unit will react with twoatoms of sulfur as follows:

...tis ig i c .analisi and the product obtained is identical in all itsproperties with that shown in Equation F in the diagram.

This is further proof that the organic radicals in the polymer, i. e.,the carbon radicals, are

joined together through a bridge of two sulfur atoms. This bridge is intlrm chemical combinavention, a vulcanizable natural or synthetic rubberis intimately mixedwith a polymer of the unit` [fw-si I I represents twocarbon atoms joined to and separated by structure selected from thegroup consisting of ether linkages, unsaturated carbon atoms, arylgroups and saturated hydrocarbons, S is a sulfur atom and n is aninteger of 3 to 6.

Upon heating, reaction occurs between the rubber and the polymer` and asa result of this reacwhere tion a novel composition is obtained havingcertain highly desirable properties as hereinafter more fully setforth.Although the vulcanization of the rubber by the labile sulfur off thepolymer is one of the features ofthe reaction, it is not limited to thisbecause the polymer as a whole alsok reacts and confers upon theresulting composition said desirable properties.

The invention will be further described in reference to the followingspecinc examples, which will be submitted for purposes of illustrationrather than limitation.

Production of poLvsulde polymer by reaction between an alkalinepolysulnde and an organic compound having a saponiflable acidicsubstituent attached to each of two different carbon atoms where thosecarbons are separated by an ether linkage. Y

Into a closed reaction tank suitably equipped with stirring means, pipecoils for steam and cold water and a thermometer are placed 2,000 litersof 3-molar sodium tetrasulflde solution. To the I polysulflde solutionare added, with vigorous agitation, 10 kilograms of caustic sodadissolved in 15 liters of water. 'I'his is followed by the addition of25 kilograms of crystallized magnesium chloride (MgClzHaO) dissolved in20 liters ofwater.

. The polysulilde mix is heated to about 135 F. and about 700 kilogramsof BB' dichloroethyl ether are added gradually over a period of aboutthree hours. The rate of addition of the dichloroether is so regulatedas to prevent the temperature of the reaction from going above about 210F. during the reaction. i

When all the chloroether has gone into the reaction and the temperatureshows a tendency to drop, steam may be admitted to the heating coilsand/so regulated as to maintain a temperature of from 215 to 220 F. forabout three hours during which time the latex-like dispersion of thepolymer is constantly stirred or agitated. .The heating step justdescribed is carried out in order that the excess of polysulde over thatactually required to decompose the dichloroether may exert a condensingor polymerizing effect on the reaction product as first formed.

'I'he finely divided latex-like dispersion of the polymer may now befreed from water-soluble impurities by any suitable means such asfiltration and repeated washing with fresh water, or it may be washed byrepeated settling of the particles, removal of supernatantliquidfollowed by re suspension in r clean water and the settling processrepeated.

'Ihe washed latex-like dispersion may now be used in the dispersed formor it may be separated from excess water by filtration and drying togive an elastic mass; or it may be treated with Sufficient dilute acid,for example dilute hydrochloric, sulfuric or acetic acid, to confer aslight acidity on the latex dispersion in which. case coagulationoccurs.

'I'he coagulum can be freed from adherent and occluded water bymastication or kneading on rolls or by prolonged drying or by subjectingto pressure.

It-will be noted that in the above example six kilogram mols of thepolysulfide were used whereas only about ve kilogram mols of the organicreactant were used leaving about 20 molar percent excess of thepolysulde. This procedure provides an excess of polysuliide over thatrequired for saponincationlof the organic compound used and that excessis then immediately available for the second step which results infurther polymerization of the product due to the oxidizing effect of thepolysuliide on the iinely divided reaction product during the prolongedheating period. t

Equimolecular proportions of the organic reactant could obviously beused with the polysuliide and after the saponication is complete anadditional treatment with more polysulfide could be made. Or the latexcould be washed and then further polymerized by treatment with a currentf air. Substantially the same result is obtained finally 'but the methodgiven is considered the nost convenient and economical especially inview of the fact that the excess of polysulde can be recovered ifdesired.

It is sometimes advantageous when using the ester-type of organicreactant to substitute all or part of the water used in .the reaction byalcohol. This alcohol may be very completely recovered from the spentreaction liquid as the J polymer is usually only slightly solubletherein.A

In the above example, instead of BB' dichloroethyl ether, any memberselected from the following lists can be employed, using tl'ieK samemolecular proportions.

Class A.Wherethe carbon atoms (to which the reactive substituents are`Joined) are attached to and separated by atomic structurecharacterized'by an ether or thlo ether linkage. (Esters are included inthis class.)

` X.C:H4.O.C2H4.X' di-substituted ethyl ether.

` xcmocmx' dl-substituted methyl ether.

XC2H4O.C:H4.O.C2H4.X

di-'substituted-v ethoxy ethyl ether.

' X. C2H4.S.C2H4.X'

ii-substituted thloethyl ether.

cli-substituted thlo methyl ether.

CH: xmomcmocmx' di-substituted 1,3 methoxy, 2,2 dimethyl propane.

X.CH3.CHz.CHz.O.CH.z.O.CHz.CHz.CHa.X' di-substituted dlpropyl formal.

X.CII2.CH2.O.CH2.O.CII2.CII2.X'

d-substituted diethyl formal.

Xmomxsmocn.

di-substituted dlmethoxy ethane.

cli-substituted para. diethoxy benzene.

X.CHzO.Cm.CHz.OCHz.X

ii-substituted dimethoxy ethane.

X.CH2.CHz.CHz.S.CHa.CHa.CH2.X'

di-substituted dipropyl thio ether.

x.oH,.cH,.o.c.o.cH,.cH|.X'

di-substituted dlethyl carbonate.

2.CH3.(|.|7.0.CH2.CH:.O.("J.CHz.X dl-substituted glycol diacetate.

di-substituted trimethylene glycol dipropionate.

Class B.Where the carbon atoms (to'which the reactive substituents arejoined) are attached to and separated by structure characterized byunsaturated carbon atoms.

X.CH:.CH=CH.CH2.X'

1,4 di-substituted butane 2.

1,6 dl-substitllted hexelle 3.

1,4 di-substituted pentene 2.

1,6 1i-substituted heptene a.

,class c.-Whe'rethe carbon atoms (to which the reactive substituents arejoined) are attached to and separated byA aromatic structure or an 15aryl group.

AA disubstituted naphthalene CHX' XCR@ 25 Ha 1 l j disubstitutedmesityleno can: (I) v ao Bix' v 1,4 dlsubstituted naphthslene asXQCHLCHQX' para bstitutd dibenzy 1,4 substituted mamans 45 XCHOCHLX'para disubst tuted toluene v l0 .XOX'

para substituted man l X' 55 X@ mno aisubmuted benzene x'cH XCH

orthov disubstitutcd xylene substituted pm aiszhyibengen 1,4dlsubstituted naphthalene Classl D.Where the carbon atoms (to which 75 Ithe reactive substituents are joined) are attached to and separated bystructure characterized by saturated carbon atoms or methylene groups.

X.CH2.CH2.CH2.X'

X.CH2. (CH2) .X

(n may be 1 to 20 or more) oH3.omomomoncmom it )if xcmoaomx' (llHaxomcacmx' en, on,

EXAMPLE II Preparation of a disulfide polymer by oxidation of apoli/functional mercaptan.

138 pounds or 1 mol of dimercapto ethyl ether, SH.C2H4.O.C2H4.SH, aredissolved in 100 gallons sodium hydroxide solution containing lbs. ofNaOH; that is, an amount of NaOH slightly in excess of 2 mols. With thissolution there is intimately mixed a freshly prepared suspension ofmagnesium hydroxide made by treating 10 pounds of MgCl2.6H2O with 2gallons of water` and adding thereto a solution of 4 pounds NaOHdissolved in 0.5 gallon of water. 'Ihe entire mixture lis then placed ina reaction vessel provided with stirring means and also means forheating, for example, steam coils. The mixture is subjected to stirringand to this is gradually added an oxidizing agent in the form of asolution of sodium polysulde made, for example, by dissolving 348 poundsor 2 mois of sodium tetrasulflde in 1 liter of water during a period ofabout ten minutes. 'I'he reaction occurs approximately at roomtemperature and is somewhat exothermic. The reaction is substantiallycompleted after all the polysulde has been added. 'Ihe completion of thereaction is indicated by withdrawing a sample, acidifying it andobserving whether the odor of mercaptan is absent. Stirring may becontinued until the reaction is completed as indicated by this test.

. The polysulde acts as an oxidizing agent and converts :the dimercaptoethyl ether into a complex polymer or plastic. The advantage of themagnesium hydroxide is that the said polymer or plastic 'is produced inthe form of a latex-like liquid which has the unique property of beingcapable of intimate mixture with water and settling out subsequently bythe action of gravity. This property permits intimate and thoroughwashing to remove soluble impurities. Acidication of the latex-likeliquid causes the separation of polymer as an agglomerated mass, theremoval of the impurities from which would be a diiiicult problem. It istherefore highly desirable to accomplish the washing while thismassriswin dispersed form, inasmuch as under such conditions the highdegree of dispersion of the polymer permits an extremely thoroughremoval of the soluble impurities by washing. The difculty oftransporting the latex in agglomerated form, and the ease with which itsticks to parts of apparatus, such as the stirrer, also makes itadvisable to produce the polymer in the reaction vessel in its dispersedlatex-like form, from which vessel it can be readily removed because ofits iluid characteristics. If the polymer were produced in the reactionvessel in its coagulated rubbery form it would be difficult to remove ittherefrom and it would be contaminated with the reagents used in itsmanufacture- Washing of the polymer in its dispersed condition may beaccomplished in the reaction vessel by stirring it up with successivequantities of water, settling and drawing '0R the supernatant washliquid. The washing can, of course, be accomplished in a differentvessel. In any event, it is desirable to preserve the polymer in itsdispersed .condition until after removal from the reaction vessel.

The washed latex is then transferred to a secondvessel where coagulationor agglomeration is produced by acidification. Suilicient acid may beadded for this purpose until the mother liquid is acid to methyl orangeor brought to a pH.' of about 3`. The coagulated polymer is thendehydrated by any suitable method, e. g. milling, mastication, orkneading. In such processes, considerable heat is generated which,together with the mechanical action, causes the removal of water.

In the above example, instead of sodium hydroxide as the agent fordissolving the dimercapto compound, other alkalinehydroxides could beused, for example, potassium, ammonium, lithium, calcium, barium,strontium, and in generalv any other alkaline materials which will notform highly insoluble sulfides.

Instead of magnesium hydroxide, other gelatinous hydroxides may beemployed, for example, aluminum hydroxide, chromium hydroxide, ferriehydroxide; moreover, dispersing agents other than hydroxides may beemployed, for example, gelatin, albumin, casein, agar, soluble celluloseesters, etc.

Instead of sodium polysuliide, other polysuldes may be employed, e. g.potassium and ammonium polysulde or any other soluble polysulilde. Otheroxidizing agents may be used, for example, oxygen, air, ozone,hypohalites, andin general any oxidizing agent eilective in an alkalinesolution, for example, hydrogen peroxide, and metallic peroxides,perborates, chromates, dichromates, manganates and permanganates, etc.The reaction is preferably carried on under alkaline conditionsbecause'it has been found that the reaction is very favorably inuencedby such conditions.

Although in the above example, the step of agglomerating or coagulatingthe polymer was speciiically described, it is in some cases advantageousto preserve the polymer in its dispersed form as such, e. g. for use incoating and impregnating various materials.

In Example IV, instead of dimercapto ethyl ether, any member selectedfrom the list hereinabove set forth can be employed in the samemolecular proportions, where X and X' are, respectively, an SH group, asillustrated in Example IIa.

' EXAMPLE IIA 210 grams glycol dimercapto acetate l?nsouz.c.o.C1I2.C1Ii,0amsn prepared by reacting glycol dichloroacetatewith an alcoholic solution of potassium hydrosulflde,

are dissolved in two liters of cold molar sodium hydroxide.

grams MgClzHzO are dissolved in 100 cc. water and 100 cc. of solutioncontaining 15 .grams NaOI-I are mixed with the magnesium chloridesolution. The gelatinous mass of Mg(OH)z is. thoroughly mixed with themercap- .tide solution.

Reaction of disulphide polymer with elementary sulfur to producepolysuljde polymer One mol of the unit .of which the polymer is composed(which in Example IV is -C2H4.O.C2H4.S.S-)

or, in Example V -CHzC.O.O.C2HAO.O.S.S.S. is mixed with two atomicweights of sulfur and then heated to about 250 F. for one hour,preferably with the addition of about 0.2 part by weight ofldiphenylguanidine and 5 parts by weight of zinc oxide. The productobtained is substantially identical with that obtained in Example* I asregards its Vulcanizing power for and reaction 'with natural andsynthetic rubber,l e. g. the

butadiene polymers.

In practisingv the invention, the polysulfide polymer may be mixed withthelcompound to be vulcanized, e. 'g. natural rubber, or vulcanizable'synthetic rubber, in any suitable manner and the mixture then subjectedto a heat treatment to cause reaction to take place. This procedure willbe illustrated in the following example:

EXAMPLE IV Parts by Ingredients or compounds weight Polysulde polymer,as produced in Example I or III. 5 Natural rubber, smoked sheets Zincoxide 5 Carbon black.. 45 Pine tar 355 Stearic acid 2 Mercapto benzothiazole (Captax) l 'I'he above ingredients were mixed by mastication ona rubber mixing roll and then subjected to a temperature of 274 F. for aperiod of 90 minutes in a heated mold.

The properties of the resulting cured product will betabulated below incomparison with those of a 'product similar in all respects except thatelementary sulfur was used as the vulcanizing agent instead of thevulcanizing agent of this invention. IThe control mixture usingelementary sulfur as the vulcanizing agent was made up as This controlcompound was cured by heating to a temperature of 274 F. for 90 minutesin a heated mold.

'I'he properties of the products produced las in Examples II and III maybe contrasted as follows:

Pounds per square inch The above comparison shows that. whereas the twomoduli given indicate about the same stiiI- ness of the two examples,the tensile strength in the case of Example -IV 840 pounds greater, i.e. more than 25% higher, than the control cured in the ordinary manneras in Example V, and the elongation is also greater in the case ofExample V.

Experiments covering a considerable period of time have shownconclusively in all cases that in the sulfur cures where a suilicientamount of sulfur was used to eifect the optimum cure (as in Example V),a definite blooming of the excess sulfur to the surface sets in in fromthree to six months, depending somewhat on the conditions under whichthe specimens are stored, whereas, in no case, even over a period of ayear, has any evidence of blooming taken place where the cury ing agentwas of the type set forth in this into convert it toa polysulildepolymer, the sulfur so reacting being converted into a labile form.

This has been illustrated by Examples I, II

and III.

Instead of first preparing an organic polysulfide, by any of the methodsabove set forth, l

and employing that as such, as a. vulcanizing agent, I may rst prepare adisulfide polymer, mix the same with a suitable proportion of elementarysulfur and employ the mixture as a vuicanizing agent. This will beillustrated by the following example:

EXAMPLE VI Vulcam'zing by means of al disulfide polymer and v The abovecompounds were cured 50 minutes at 287 F.

Physical properties A B Tensile strength lbs. per sq. inch 3100 3980Elongation at brcak .pcr cent.. 800 890 When examined at the end of sixmonths, sample A had bloomed considerably and vincipient checking wasevident when the sample Awas stretched.

Example IV Example V 100% modulus pounds per square inch.. 245 235 300%modulus d 107,0 1050 Ultimate tensile strength do 4350 3510Elongation... per cent.- 670 635 Set 47 40 Hard ness 63 63 Chlorbutadiene 100.0 100.0 Sulfur 3. None Tetrasultde polymer produced as inExamples I and III None 5. 0 Y Light calcined magnesia i 10.0 10. 0Cottonseed oilV 10. 0 10. 0 Carbon black 35. 0 35.0 Zinc Oxide 10. 0 10.0

Cure 40 minutes at 307 F.

Physical tests I C D Modulus at 300% elongation 400 515 Tensile strength'.lbs. per sq. in 2700 3110 Elongation at break .per cent.- l 870 900The use of the tetrasuliide polymer (in this Example B showed no traceof bloom nor did itexhibit any trace of light checking on ilexure orstretch.

Physical tests after 6 months aging.

Tensile strength -l ..1bs. per sq. inch.. 22m asso Elongation at breakper cent.- 730 840 It will thus be apparent that freedom from bloomingis not the only advantage gained by practising the present invention andlthat new compositions having other improved properties, are obtained.

Various synthetic rubbers, such as those pro-` duced by polymerizationof butadiene, chloroprene (chloro 2, butadiene 1,3) etc. maybe cured orvulcanized by elementary sulfur, but such vulcanizates tend to bloomvery badly upon standing or storage. The present invention makes it pos-EXAMPLE VII example, the tetrasulide derivative of ethyl ether wasused), gave a vulcanizate having, depitely enhanced physical properties.Moreover, when the stocks were examined after Vsix months aging, thesulfur core showed a denite crystalline bloom, whereas D had a polishedblack surface apparently entirely unchanged.

EXAMPLE VIII Cure 40 minutes at 307 Physical tests E F Tensile strengthlbs. per sq. in.. 2110 2360 Elongation at break per cent. 550 590Examination at the end of a six months period showed E to have a powderybloom on the surface from which F was entirely free.

In Examples VII and VIII. s.' mixture of 1 to 4 atomic weights of sulfurwith a mol of the polymer of the unit I. .,tss]

could be used instead ofthe tetrasulide polymer specifically mentionedin said examples, the carbon atoms of that unit being Joined to andseparated by suitable structure as described.

It is of great advantage to be able to vary the rate of vulcanizationindependently of the per cent of sulfur combined or coeillcient ofvulcanization. The ideal condition is to havey a vulcanizing agent whichitself possesses no accelerating action and toobtain the desired c0-eicient by regulating (1) the time, (2) temperature and (3.) nature andconcentration o! accelerator, (1), (2) and (3)- being capable ofvariation independently of the vuleanizing agent. The vulcanizing agentsof this invention very closely approach this ideal. This means that ifthe time and temperature are xed, the' coeicient of vulcanization can becontrolled solely by controlling the nature' and concentration oiacceleratordn the presence of a predetermined or iixedl concentration of-vulcanizing agent. Inde-` eflcients of vulcanization may be necessaryfor' the same rate of cure. This independence of control is provided bythe present invention.

For example, in a composite rubber article, such as a tire casing, toobtainy the necessary variation in properties of the respectivecomponent's, it is necessary to control the rate of curing independentlyof the coemcient oi vulcanlzation. This cannot be done if thevulcanizing agent possesses active accelerating ability and ii' thisability is in a xed ratio to its combining power for theV rubber.k

To some extent sulfur possesses this vulcanizing power independent ofaccelerating effect but combination of sulfur and accelerator have atleast two markeddisadvantages. First, they are subject to the phenomenonof reversion accordingv to which the elongation. and tensile strengthreach a maximum and then decrease so that great care must be taken notto pass this maximum. Frequently this maximum cannot be attained as forexample in composite articles which` must be cured at the sametemperature and for the same period, where the component t parts havedifferent rates of cure.

On the contrary, combinations of the vulcanizing agent of thisinvention'with accelerators are free from the phenomenon of reversion.Consequently tensile strength and elongation do not decrease afterreaching a maximum.

In support of the above statements, regarding independence between rateof vulcanization and coecient, and freedom from reversion, the followingdata are submitted:

EXAMPLE IX Smoked sheets Tetrasuliide polyni r Zinc oxide Stearic acid.

The above products A and B were then cured and the cured products testedas shown below:

Cure

Mglus Tensile Elongat lon Sample Min. Temp.

F. 30v 287 330 lbs. 3000 R50 B 60 l287 450 lbs. 3110 810 B 9() 287 470lbs. 3000 790 B 120 287 490 lbs. 2980 780 B 120 298 N o-cure A 180 29820 125 930 A 240 298 30 200 940 A The above data show conclusively thatthe ether tetrasulde polymer did not have an accelerating effect andtherefore can be used in suitable proportions in a sulfurlesscure forwhich any suitable degree of acceleration may be selected.

Tests in product A in which no accelerator is used show that thevulcanizing agent of this invention in the presence ofan accelerator-produces tensile strength of 3,000 pounds per square inch. in 30minutes at' 287 F. (indicating rapid cure)4 whereas in the absence of anaccelerator only ,200 pounds per square inch was obtained in 4 hours at298 F. (indicating substantially no cure)'. Therefore, with theVulcanizing agent of this invention, the rate of cure can be controlledat Will by selecting the kind and concentration of accelerator. By usinggreater or smaller proportions of accelerator than that shown in Ex'ample DI, or by using accelerators more or less powerful than thatshown'in Example IX, higher or lower rates of cure could be obtained.

In Example IX, B, the coeicient obtained was about 3 per cent. This wasobtained in 30 minutes by one per cent of mercapto benzo thiazole.Thesame coelcient is obtained in 'l0 minutes at the same temperature .by0.25 per cent, demonstrating further that-the rate of cure can be variedindependently of the coefficient.

Referring againto the above curing data, it will be noted that themaximum strength was obtained in 30 minutes. .This strength was notdecreased (within experimental error) by continuing the cure to a periodof 120 minutes.

Moreover, when sulfur is used, an excess is required over thatwhichcombines and this excess brings in its train a number of disadvantages,

e. g. blooming, poor aging qualities in air and sunlight and especiallyat somewhat elevated temperatures.

In contrast to this, the vulcanizing agents ofv mentioned,the'vulcanzing agents of this invention 4possess vulcanizing powerindependent of accelerating effect, this independence being even moremarked than in the case of sulfur.

This permits the selection and use of any suitable degree ofacceleration by selecting a particular accelerator and using it, incontrolled concentration, in conjunctionwith the vulcanizing agents ofthis invention. v

Among these accelerators the following may be mentioned:

Benzothiazyl disulfide Mercaptobenzo thiazole Diphenyl guanidneTetramethyl thiuram disulfide Di-orthotolyl guanidine Ethylidene anilineI claim: 1. A vulcanizable composition comprising a vulcanizablerubberand an organic polymer of l l C....C l l where represents twocarbon atoms joined to and separated by intervening structure and S is asulphur atom, the said polymer containing combined f sulphur availablefor causing vulcanization of the rubber and the proportion of saidpolymer to the rubber being from about 5 to 7.5 parts by weight ofpolymer and 100 parts by weight of rubber.

2. A vulcanized rubber composition comprising the reaction product of avulcanizable rubber and an organic polymer of the unit (11S: r0.0] l l ll C C l l represents two carbon atoms joined to and separated byintervening structure, the proportion Where of said polymer being fromAabout 5 to '7.5 parts Where l l C...C c

lv I

represents two carbon atoms joined to and separated by interveningstructure and S is a sul-` phur atom, together with a predeterminedproportion of `a substance which accelerates the vulcanization of rubberby sulphur, the propor tion of said polymer to rubber being from about 5to 7.5 parts by weightof polymer to 100 parts by weight of rubber andeffecting vulcanization by heating the compound. y

f JOSEPH C. PATRICK.

